Please debate between the following transformation
Giant namek transformation (warriors and dragon clans)
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(Increases defences, max LP/EP and attack power big time, duration is however only 10 minute.
Aswell opens acces to 2 skills, however unable to use other skills (there are few exceptions such as agro, armpull and staff slash)
Kid buu transformation (wonder majins and mighty majins)
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Increases attack power, becomes ranged , unlocks 2 other attacks, locking other skills
Duration is infinite, drains EP.
Super saiyan transformation (Martial artists and spiritualists)
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Increases attack power, dodge,attack speed, running speed, hitrate, max EP.
Remain able to use all your skills, drains EP.
Duration is infinite
I dont include kaioken since everyone has it.
My own input
Personally i think Giant namek is for me personally, one of the most effective transformations.
as a ShadowKnight i can manage to get the cooldown to this.

And with a 10 minute duration, the time i have to wait between transformations is merely 8 minutes.
The transformation is really good in PvE situations with a team for stuff like cell or bacterian.
I do realize its only good for SK if you have speed weapons and dogi hat.
Wich i do, so im using this transformation alot in PvE situations.
Its like a giant namekian using thunder, wich is just epic for tanking and killing cell/bacterian.
The plus side it has over SSJ and kid buu, is the huge defence and LP increase.
Combined that with seriously huge DPS (100% speed) its for me the most powerfull transformation.
Downside is the 8 minute waiting time ''between giant'' transformations, but thats not a issue for me.
The PvP aspect of this transformation is usefull too.
It can be used in 5v5 situation when your entire team is ... dead and you need to buy some time to resurect everyone.
Aswell it can be used to get rid of all de-buffs, to give you a small window of oportunity to get a advantage, other then this, it doesnt really gives a advantage for a SK.